Wire terminals



A. R. NORDEN WIRE TERMINALS Dec. 17, 1968 2 Sheets-Sheet 1 Filed July 6,1966 Dec. 17,1968

A. R. NORDEN v WIRE TERMINALS 2 Sheets-Sheet 2 Filed July 6, 1966 5 M 3I M WM 1 3 0 l a 4 3 I 5 m1 6 /H 5 ||1 H 1M2 11 4 W i b w W! l e I I 35. 3 l 2 w {I a a 3 United States Patent 0 3,417,368 WIRE TERMINALSAlexander R. Norden, 350 Central Park W., New York, N.Y. 10025 FiledJuly 6, 1966, Se!- No. 563,248 24 Claims. (Cl. 339-147) ABSTRACT OF THEDISCLOSURE A wire stripper is provided having cutting edges of aplastic, especially nylon, that is harder than polyvinylchlorideinsulation but softer than wire to avoid making a nick in the wire; andto special advantage the plastic of the wire stripper forms part of theelectrical insulation in an electrical device having at least onewire-securing terminal.

Generally, the present invention is concerned with devices for making anelectrical connection to the end of a wire, and to strippers forpreparing wires for such connection.

A widely used type of wire connection involves no screws, andcharacteristically depends upon a leaf-spring wire-retainer that isdisposed at an acute angle to the wire-insertion path. During insertion,the wire is simply pushed into position between the leaf-spring and anelement opposite the spring. The end edge of the leaf-spring is biasedagainst the wire. In case of pull on the wire, the edge tends to diginto the wire. The spring provides the reaction force resisting removalof the wire. Due to the acute angle of the leaf-spring, the reactionforce extends essentially along the spring. This arrangement is suchthat very large pull forces are inherently resisted by the leaf-spring.

Wire terminals of this form have proved highly successful where solidwire is used, but they are not well suited to use with stranded wire.Individual strands of a stranded wire tend to bend to one side when aneffort is made to insert the wire. In another manner, the bundle ofstrands at the end of a wire being inserted may not have enough strengthto deflect the spring, with the result that the bundle of strands simplycollapses, mushrooming as it is being pushed. To overcome this effect,the leafspring might be made especially soft for accommodating strandedwire. In that case there is danger of the leafspring being deformed,even buckling, when the wire is subjected to pull which the connectionshould resist.

An object of the present invention is to provide an improved wireterminal of the foregoing type, that is effective not only with solidwire but also with stranded Wire.

A further problem arises with this type of connection. For example, awire is inserted and a casual pull test is to be made. I have discoveredthat limited manipulation of a wire preparatory to a test often resultsin the wire escaping from the terminal block. Such manipulation mayinvolve twisting a wire around ones finger to be sure of a good grip. Bylike token, there is a certain amount of working of wires near aterminal in normal use, which the terminal should resist. Accordingly, afurther object of this invention is to improve wire connections of thistype, for more effectively resisting a tendency of the wire to beself-releasing when manipulated.

A preparatory step in the use of the foregoing type of terminal blocksand other types of terminal blocks is to strip insulation off the endportion of the wire. Wire strippers of conventional form represent atool that may not be readily available. Furthermore, conventional wirestrippers tend to nick the wire. A relatively slight incision into thewire that is often produced by the sharp edge Patented Dec. 17, 1968 ofthe cutting element in conventional wire strippers can be a seriousmatter. Particularly when subjected to vibration, such an incision tendsto propagate in time and may ultimately cause breaking of the wire.

An important feature of the present invention is the provision of anovel improved wire stripper integral with a terminal block and thus onethat is always readily available. More generally, a further object ofthe invention resides in providing a novel wire-stripper forplasticinsulated wire, of a form that entirely eliminates the danger ofcutting into a wire incidental to cutting through the insulation.

The foregoing objects, and others that will be apparent, are achieved inthe illustrative novel terminal block that is shown in the accompanyingdrawings and described in detail below. In this terminal block there arepl-ural groups of wire-receiving guide passages, each group being forwires to be connected to each other. For each group of passages (threeto a group in the example shown) there is an internal metal strip thatis relied on primarily for the electrical connection. A leaf-springmember has separately resilient portions for biasing inserted wiresagainst the metal strip. Each leaf-spring portion inclines toward thewire and extends along the wire in the direction of insertion, formingan acute angle to the wire. The edge of the leaf-spring at the end ofeach wire-engaging portion tends to dig into the wire when resistingpull applied to the w1re.

Such arrangements are well-known. I have found that they tend to preventproper entry of stranded wire and to cut through thin multi-strand wirewhere the leaf-spring is firm, or there is a danger of the leaf-springbuckling w-hen moderate pull is applied to the wire in the case ofsofter leaf-springs designed to accommodate stranded wire. This issolved in the illustrative terminal block by providing two leaf-springelements that engage each wire at different acute angles at differentpoints along the wire, in an arrangement wherein pull on the wire tendsto develop tension between the points of engagement with each wire. Thisarrangement provides assurance that any pull imposed on the wire isshared between the leaf-spring elements. Were two (or more) leaf-springelements used in simple face-to-face parallelism, there would be atendency for one element to take the whole load of the wire pull, sothat such an arrangement would be of doubtful benefit as compared to asingle leaf-spring element.

Where leaf-spring elements engage stranded wire, any twisting of thewire (I have found) tends to form a longpitch helical indentation in thewire and pro-motes selfrelease of the wire. By forming fine-pitchserrations in the wire-engaging edge of a leaf-spring element, thisturning of the wire is actually prevented. The close-spaced teeth findplaces in the stranded cluster of wires. Such a wire terminal isremarkably immune to the aforementioned self-releasing tendency thatcharacterizes the type of leafspring terminal connection here involved.

Preparatory to each wire insertion, a measured length of the wire shouldbe stripped of insulation. An important feature of the present inventionresides in the utilization of the same material that forms theinsulating body of the terminal unit not only for its electricalinsulating qualities, but also as an insulation stripper having theunique property of eliminating the problem with conventional strippersof nicking the wire incidental to cutting through the insulation.Insulation for the terminal block can readily be selected that is softerthan wire yet not so soft as to be rubbery, Such insulation can beformed into a cutting edge for making incisions into vinyl and othercommon types of plastic wire insulation. The cutter in the illustrativeembodiment is a V-notch in an insulating wall, the edges of the V beingsharp enough so that when plastic-insulated wire is pressed into theV-notch, the wire insulation is cut through and yet the wire itself isimmune to incision. A pull on the wire at this time strips theinsulation from the wire, which is then in condition for use in theterminal block.

The nature of the invention will be more fully appreciated, and otherobjects and advantages will be recognized, in the following detaileddescription of an illustrative embodiment of the invention in itsvarious aspects.

In the accompanying drawings:

FIGURE 1 is an enlarged perspective view of an embodiment of theinvention in its various aspects;

FIGURE 2 is a plan view of the embodiment in FIG. 1;

FIGURE 3 is a fragmentary cross-section of the device in FIGS. 1 and 2viewed from the plane 3--3 in FIG. 1;

FIGURE 4 is a greatly enlarged fragmentary vertical cross-section of thedevice in FIGS. l-3 as viewed from the plane 4-4 in FIG. 2;

FIGURE 5 is a greatly enlarged perspective of a leafspring memberforming part of the device in FIG. 4; and

FIGURE 6 is a diagram illustrating a feature of the action of theleaf-spring elements on a wire when subjected to pull.

In the drawings, FIGS. 1, 2, 4 and 5 show a six-circuit terminal block10 comprising two parts 12 and 14 of molded insulation. Walls 16a, 16b16 extending across the top insulating part 14 are barriers that dividethe unit into six separate circuits. For each circuit there is a groupof three wire-receiving guide passages 18 (FIG. 2). At each end of eachwall 16 there is a hook 20 that holds an inserted wire in a right-angledform to tailor into a neat arrangement the cluster of wires entering theterminal block.

The lower part 12 has a pair of lateral ribs along its opposite sides,for interlocking retention by in-turned hook formations 26 formingintegral parts of a mounting strip 28 as of extruded aluminum. Ribs 22are on wall portions of insulating part 12, the wall being defined bygroove 30. The material of parts 12 and 14 is a relatively firm yetyieldable plastic exemplified by nylon. Thus, when block 12 is pushedagainst mounting strip 28, ribs 22 snap under hook formations 26 forsecure retention. Still, when release becomes necessary, rib 22 iseasily pried free of hook 26.

Upper part 14 of the two-part insulator assembly has two rows of lateralprojections 29 at its opposite sides for entering corresponding holes 31in lower part 12 for locking those parts together. The lower faces ofprojections 29 slant upward and outward. When parts 12 and 14 are to beassembled, they are forced together, the side walls of part 12 spreadingoutward until parts 29 are aligned with holes 31 whereupon the sidewalls snap together to retain projections 29 in holes 31.

As best shown in FIG. 4, each wall portion 16 has a shoulder 33 thatholds a metal connector strip 32 as of copper in place below a row ofguide passages 18. A leafspring member 34 is captive in a pocket 35 ineach wall 16, and provides three pairs of wire-engaging elements 36 and38. These pairs of elements are spring-biased laterally againstrespective portions of a companion connector strip 32. The wire-engagingedge of each element 36 is serrated, having several close-spaced teeth36a for locking into fine-stranded wire W.

As seen in FIG. 4, each pocket 35 locates a member 34 in positiondespite outward pull on a wire W that is gripped between connector strip32 and leaf-spring elements 36 and 38. Member 34 has an off-set portion40 (FIG. 5), one part of which bears against insulation portion 42 whenan inserted wire is pulled. When this occurs, the different acute anglesof elements 36 and 38 tend to cause those elements to swing throughshort arcs shown with exaggeration in FIG. 6 to positions 36' and 38.The are of element 36 involves a longer component of motion along thewire than that of element 38. Consequently, the points of engagement ofelements 36 and 38 with the wire which start with separation A tend tospread apart to a larger separation A when a wire is being pulled. Thegreater separation A signifies a tendency of stretch to develop in thewire, and signifies pull in the wire imposed by element 38. This is partof the total pull on the wire, and demonstrates sharing of the pullbetween the leaf-spring elements. Each leaf-spring element picks up someof the pull and thus contributes to effective wire retention.

As illustrated, three wires W (FIG. 1) can be inserted into the guidepassages 18 of a single circuit, to be interconnected by conductingstrip 18. To a degree, member 34 also interconnects the wires W. Inother devices using one or more pairs of leaf-spring elements 36 and 38,the connection established may extend to other apparatus in such devicesrather than to establish interconnection to other wires in the formshown. The term wire terminal is used to refer not only to terminalblocks but also to other devices having electrical connections.

Wires for the class of the terminal block illustrated and for otherelectrical devices are commonly covered with a pliable plasticinsulation such as polyvinyl chloride. The end portion of such a wire iseffectively bared by a stripper forming part of the terminal block,including a gage stop represented by wall 16d that is higher than itsneighbors, and a V-notched projecting wall 16a. This wall presents aflat face toward gage-stop wall 16d, and the sharp-edged V-notch 50 isthen effective to cut into the plastic insulation on a wire W whenforced by hand into the notch. The acute angle a (FIG. 2) is madesuitably small for making an incision into plastic insulation but toosmall an angle would make the edge feathery and weak. After being firmlypressed to the bottom of the V- notch, a wire W is firmly pulled in thedirection of the arrow in FIG. 1, to strip the accurately measuredlength of insulation between walls 16a and 16d.

Parts 12 and 14 are of a relatively hard form of nylon, in a preferredapplication of the invention, nylon having excellent properties as anelectrical insulator and being harder than plastics used as insulationon wire so as to cut that insulation for stripping the wire yet notbeing so hard as to make an incision. Where nylon is the material usedas the electrical insulation, an effective hardness of the material atthe wire-stripping V-notch is Rockwell Scale R to 118.

The foregoing illustrative embodiment of the invention in its variousaspects is readily susceptible to varied application and modification bythose skilled in the art, and therefore the invention should be broadlyconstrued, con sistent with its full spirit and scope.

What is claimed is:

1. A wire stripper including a pair of opposite portions having cuttingedges arranged to penetrate the insulation of plastic-covered copperwire, said opposite portions being of a plastic softer than copper forprecluding the formation of an incision in the wire, and a gage stopdisposed at a distance from the cutting edges that equals the length ofwire to be bared.

2. A wire stripper in accordance with claim 1 wherein the surfaces thatmerge to form each of said cutting edges have an acute angletherebetween.

3. A wire stripper in accordance with claim 1 for wire havingpolyvinylchloride insulation wherein said opposite portions are of aplastic harder than polyvinylchloride insulation.

4. A wire stripper in accordance with claim 1 wherein said cutting edgesare formed of nylon.

5. A wire stripper in accordance with claim 1 wherein said cutting edgeshave a Rockwell hardness on Scale R of approximately 110 to 118.

6. A wire stripper in accordance with claim 1 wherein said cutting edgesare of nylon and have a Rockwell hardness on Scale R of approximately110 to 118.

7. A wire stripper in accordance with claim 1 wherein each of saidcutting edges has surfaces merging at an acute angle and wherein theplastic has a hardness on Rockwell Scale R of approximately 110 to 118.

8. A wire stripper in accordance with claim 1 wherein said oppositeportions are converging parts of a notch formed in a one-piece plasticmember.

9. Apparatus in accordance with claim 8, wherein said wire stripper ispart of a wire terminal comprising metal wire-securing means and whereinsaid plastic member is of electrical insulation arranged to support saidmetal wire-securing means.

10. Apparatus in accordance with claim 8 wherein said wire stripper isan integral part of an electrical terminal block having wire-securingparts electrically insulated by upstanding walls one of which is saidone-piece plastic member having said notch therein, another of saidwalls being a gage stop spaced from said one wall by a distance thatequals the length of wire to he hated.

11. Apparatus in accordance with claim 8, wherein said wire stripper ispart of a wire terminal comprising metal wire-securing means and whereinsaid plastic member is of nylon arranged to support said metalwire-securing means.

12. A wire terminal comprising an electrically insulating member, andmetal wire-securing means supported by said electrically insulatingmember, said member including a pair of opposite portions having cuttingedges arranged to penetrate the insulation of plastic-covered wire, saidmember being of a plastic softer than copper for pre' cluding theformation of an incision in the wire.

13. A wire terminal in accordance with claim 12, wherein said member hasa Rockwell hardness on Scale R of approximately 110 to 118.

14. A wire stripper in accordance with claim 12 wherein each of saidcutting edges has surfaces merging at an acute angle and wherein theplastic has a hardness on Rockwell Scale R of approximately 110 to 118,and further including a gage stop disposed at a distance from thecutting edges that equals the length of the wire to be bared.

15. A wire stripper in accordance with claim 12 wherein each of saidcutting edges has surfaces merging at an acute angle and wherein theplastic is nylon.

16. The method of stripping wire having a covering of plastic insulationincluding the step of making an incision by penetrating the insulationbut not cutting into the wire using a tool having a cutting edge of aplastic that is softer than the wire.

17. The method as set forth in claim 16 wherein the wire to be strippedhas a cover of polyvinylchloride insu lation, and the cutting edge ofthe tool is harder than the polyvinylchloride insulation of the wire.

18. The method of stripping wire having a covering of plastic insulationin accordance with claim 16, in which said penetration is effected nearan end of the wire, including the further step of pulling the tool alongthe wire toward the end thereof to remove the insulation from the wirebetween the incision and the end of the wire.

19. The method in accordance with claim 16 of strip ping insulation fromwire having polyvinylchloride insula tion, wherein the insulation ispenetrated at opposite sides of the wire by a tool having oppositecutting edges of a plastic harder than the polyvinylchloride insulation.

20. The method in accordance with claim 16 wherein the material of thecutting edge is nylon having a hardness on Rockwell Scale of R to 118,approximately.

21. The method in accordance with claim 16, wherein the tool has a gagestop disposed at a distance from the cutting edge and including the stepof butting the end of the wire against the gage stop before making theincision for disposing the cutting edge properly for locating theincision.

22. The method of stripping wire in accordance with claim 16 wherein thetool has a pair of cutting edges disposed to form a V-notch, thesurfaces of the tool that form each edge having an acute angletherebetween and the incision being made by pressing the wiretransversely into the V-notch.

23. The method in accordance with claim 16, wherein the insulation ispenetrated at opposite sides of the wire by a tool having oppositecutting edges converging to form a notch and of a plastic harder thanthe polyvinylchloride insulation of the wire.

24. The method in accordance with claim 23, in which the incisions aremade near an end of the wire, further including the step of pulling thetool along the wire toward the end thereof to remove the insulation fromthe wire between the incisions and the end of the wire.

References Cited UNITED STATES PATENTS 2,306,403 12/ 1942 Mortensen819.5 3,124,021 3/ 1964 Benander. 3,220,110 11/1965 Popeil 30243,284,754 11/1966 Buchanan.

MARVIN A. CHAMPION, Primary Examiner.

JOSEPH H. McGLYNN, Assistant Examiner.

US. Cl. X.R. 33995, 198

